The silver halide emulsion for use in silver halide photographic light-sensitive materials is usually subjected to a chemical sensitization using various chemical substances so as to obtain desired sensitivity and gradation. Representative examples of known chemical sensitization methods include sulfur sensitization, selenium sensitization, tellurium sensitization, noble metal sensitization using gold or the like, reduction sensitization and various sensitization methods using a combination thereof. Recently, silver halide photographic light-sensitive materials are strongly demanded to have high sensitivity, excellent graininess, high sharpness and rapid processability with expedited progress of development and to cope with these requirements, various improvements have been made on the above-described sensitization methods.
Also, color printing papers are demanded to have enhanced sensitivity, image quality and performance at the processing, such as toughness, and to satisfy these requirements, an emulsion ensuring high sensitivity and high contrast and an emulsion reduced in the fluctuation of photographic properties due to difference in the temperature and humidity conditions at exposure are demanded. On the other hand, apparatuses for laser scanning exposure are recently widespread and therefore, suitability for short-time and high-illuminance exposure becomes one of importance performances. The laser scanning exposure is greatly characterized in that the exposure can be performed at a high speed and the resolution can be improved. However, the color printing paper to which the laser scanning exposure is applied must have suitability for unprecedentedly short-time (specifically 10−6 sec.) and high-illuminance exposure.
Among those sensitization methods, most widely and commonly used is a gold-sulfur sensitization method using a so-called labile sulfur compound capable of reacting with silver ion to produce silver sulfide and a gold compound. This method is described in detail, for example, in P. Grafikides, Chimie et Physique Photographique, 5th ed., Paul Montel (1987), T. H. James (compiler), The Theory of the Photographic Process, 4th ed., Macmillan (1977), and H. Frieser, Die Grundlagen der Photographischen Prozesse mit Silber-halogeniden, Akademische Verlagasgeselshaft (1968).
In applying a gold-sulfur sensitization to a silver halide emulsion, a method of individually adding a labile sulfur compound capable of reacting with silver ion to produce silver sulfide and a gold compound is generally used and this method is described in the publications cited above and also in Nippon Shashin Gakkai Shi (Journal of Japan Photographic Society), vol. 50, No. 2, page 108 et seq. (1987) and Journal of the Optical Society of America, vol. 39, No. 6, page 494 et seq. (1949). The gold compound and the labile sulfur compound used in the methods described in these publications are a chloroauric acid and a thiourea compound or a thiosulfate, respectively. However, use of these compounds has various problems, for example, the attained elevation of sensitivity is not sufficiently high, fogging is readily generated, the gradation is softened and the light-sensitive material after storage for a long period of time undergoes serious generation of fog. Thus, means to solve these problems is keenly demanded.
As for the method of applying gold-sulfur sensitization using a gold compound other than the chloroauric acid, methods using a gold complex of thioethers described in JP-B-38-6447 (the term “JP-B” as used herein means an “examined Japanese patent publication”) and JP-A-62-85239 (the term “JP-A” as used herein means an “examined published Japanese patent application”), a gold complex of rhodanines described in JP-A-1-147537, a gold complex of mesoions described in JPA-4-267249, or a gold complex of hydantoins described in JP-A-4-268550 are known. However, these methods all are not satisfactory for solving the above-described problems.
JP-A-4-67032, JP-A-4-75053 and JP-A-4-86649 describe gold complex compounds which, it is stated, have an effect of improving the increase of fog in aging of a light-sensitive material for a long period of time and preventing the deterioration of graininess accompanying the increase of fog. These compounds, however, all fail in exhibiting an activity enough to solve the above-described problems.
Other than these, a gelatin dispersion of gold sulfide colloid is generally known as a gold sensitizer. A preparation method of gold sulfide colloid is described in Research Disclosure, Item 37154, page 227 (March, 1995), however, if a gold sulfide colloid is prepared according to this method, as described in Nippon Shashin Gakkai Dai 15 Kai Shuki Kenkyu Happyo Kai Koen Yoshi Shu (Japan Photographic Society, 15th Autumn Meeting for Presentation of Researches, Summary of Lectures), page 26, cyan ion which is environmentally harmful is disadvantageously produced as a by-product. Furthermore, since the gold thiocyanate is sparingly soluble such that the solubility product is about 25, precipitates undesired in view of production may be disadvantageously produced.
Other than the above-described Au(I) compounds containing a monovalent gold atom, Au(III) compounds containing a trivalent gold atom, such as chloroauric acid, are also known as the gold sensitizer. The chloroauric acid is sufficiently stable in an aqueous solution but gives photographic properties insufficient in view of, for example, sensitivity, gradation, suitability for high-illuminance exposure and toughness against temperature and humidity environments at the exposure. Thus, this compound is still in need of improvements.
JP-A-4-204724 describes a method for applying gold-selenium sensitization to a silver halide emulsion, where a labile selenium compound capable of reacting with silver ion to produce silver selenide and a gold compound are separately added. This technique also incurs conspicuous increase of fog and cannot solve the above-described problems.